A Roadmap to PET Phases and Indicators
I. The Early Warning and Preparation phase of a pandemic economy starts at the time when WHO issues an early warning for virus outbreaks, and governments begin to prepare accordingly, mainly including restrictions on travel to and from known epidemic centers.
II. During the Emergency Response phase, the virus infections emerge in different locations, with even community outbreaks. Countries adopt and implement non-pharmaceutical interventions (NPIs), including closures of schools and workplaces, quarantines and social distancing, etc. Societal level human mobility declines or even plummets. In a PET graph, the starting time (Point A) is the day before people's mobility shows a clear downward trend.
III. In the Recovery phase, epidemic growth decelerates, transmissibility declines progressively, and human mobility gradually rises. The starting time (Point C) is characterized by a tipping point when the recovered individuals start to outnumber new cases in a consistent manner (i.e., a minimum of three consecutive days), which means that more capacity of the health system is released.
IV. In the Trough phase, the declining trend of mobility starts to slow down and turns into a prolonged period of fluctuating around a low level, limiting the spread of the virus from people to people. The starting time (Point B) is the end of the descending trend when people's mobility reaches a local minimum.
V. The Vaccination phase starts when WHO announces the success of the development of a new COVID-19 vaccine (Point D). Mass production is made possible, followed by equitable and speedy deployment worldwide, then the economy decouples from the pandemic.
PET tracks three types of indicators:
I. Epidemic indicators
- Doubling days of COVID-19 cases
This is the number of days that were needed for the number of to double. More precisely, it is days between the current date (the date at which the measurement is taken) and the most recent prior date at which the confirmed cases were half the current level. It is a proxy for the rate at which the virus is spreading. The larger this number is, the lower the rate of spread of the virus. If a region has no new cases, the doubling days will naturally increase reflecting the accumulation of days. Doubling days captures the macro-scale characteristics of the epidemic growth and is more stable than the doubling time estimation of the recent seven or three days.
- Epidemic tipping time
This is the time when recovered cases consistently outnumber new cases in an economy. We looked across all countries for the point at which there were three consecutive days in which the number of recoveries exceeded the number of new confirmed cases, a situation suggesting a tipping point when the critical medical capacity of a country is starting to be released. It can be thought of as a proxy for when the epidemic is starting to be controlled and the opening up agenda can be started and the economic recovery agenda pursued somewhat more aggressively.
II. Economic indicators
- Daily economic activity level
In the pandemic economy, mobility is an effective predictor of economic activity during contraction periods. Every ten percentage of reduction in mobility relative to normal condition leads to about a drop of 3.1 percentages in an economy’s output. This is used to roughly estimate the daily economic activity of each economy. This estimation is subject to errors but does capture the most important processes that influence economic activities.
- Cumulative economic losses
Daily economic activity levels from the proceeding calculation are aggregated to calculate the total losses of economic activities relative to normal condition across a period of time, e.g., a quarter.
III. Duration of PET phases
- Length of Response phase (from A to B)
- Length of Response and Trough phases together (from A to C)
- Duration of total economic contraction mode (from A to present)
These three durations, labeled on the PET curve, form a semi-hidden time dimension in the PET graphs, showing that two economies with PET curves of similar shape may be very different in their pace.
Note of methodological changes: Smoothing method for doubling days of confirmed cases has been changed from 7-day centered moving average to moving average of the latest 7 days. As a result, the dashed line changed from 19 to 17.5, and very small changes to the shape of PET graphs.
Last updated on June 27th, 2020
Data sources: European Center for Disease Prevention and Control, National Health Commission of the People’s Republic of China, Johns Hopkins University, Google Community Mobility Reports, Apple Mobility Trends Reports, Baidu Migration Index, Amap Traffic Index, and Wind Economic Database.